Apparatus for laser cutting a workpiece

ABSTRACT

An apparatus is disclosed for cutting a workpiece. A laser beam is directed at successive points along a workpiece surface to be cut and a sensor emits a sensing beam directed at the same successive points as the cutting beam. A beam combining device receives both the sensor beam and the cutting beam and causes downstream beam segments to be collinear with each other as they impinge the workpiece surface. The cutting is thereby able to be carried out in a single pass, and is precise, repeatable and independent of cutting depth, angle of cutting, scoring patterns, material inconsistency, material color, and surface grain variability.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 09/811,152, filed Mar.16, 2001, now U.S. Pat. No. 6,423,933.

BACKGROUND OF THE INVENTION

This invention concerns apparatus for cutting workpieces by a laser beamto remove material by vaporization. In such apparatus, the laser beam isadvanced along points forming a predetermined cutting pattern on aworkpiece surface.

A widely used method for determining the extent of material removedduring controlled cutting involves the use of triangulation type sensorsas described in U.S. Pat. No. 5,883,356. These sensors, however, due totheir triangulation operating principle, are limited in their ability toreach the bottom of the scoring produced by the cutting device. This isparticularly so for narrow, deep penetrations which may be produced bycutting devices such as lasers and cutting knives. Furthermore, due totheir offset mounting, these sensors are not well suited to measure thevarying penetration depth that occurs during scoring at a specificlocation. This is especially true if the scoring penetration is in theform of partial perforations or slots. As such, the process does notlend itself to scoring the workpiece in an adaptive control mode, whereboth depth sensing and cutting are in registry with each other toimpinge the same point on the workpiece, during the progression ofscoring of the piece.

Accordingly it is an object of this invention to provide an apparatusfor laser beam cutting in a manner that provides accurate adaptiveprocess control, single-pass processing, and lower manufacturing costs.

SUMMARY OF THE INVENTION

According to the invention, the cutting of the workpiece is accomplishedby apparatus including a source of a controllable cutting laser beam,which, based on feedback obtained from at least one sensor emitting asensing beam, is controlled in intensity together with controlledrelative movement between the laser and the workpiece, producing aprecise, predetermined cutting penetration into the workpiece along apredetermined pattern.

In this apparatus, the laser cutting beam and sensing beam emitted froma first sensor are both directed at a surface on one side of theworkpiece. A second sensor may also be positioned on the opposite sideof the piece emitting a second sensor beam in opposition to the cuttinglaser beam. A beam combining device combines the laser cutting beam andfirst sensor beam together so as to have collinear segments directed atexactly the same point on the workpiece. The cutting of the workpiece iscarried out by the laser beam while the piece is moved in apredetermined pattern relative to the laser. The depth of cutting of thework piece by the laser beam is controlled by real time feedback signalscorresponding to the depth of the cut provided by the first sensor. Todetermine material thickness remaining during cutting of each pointalong the predetermined pattern, real time feedback from the secondsensor can be provided combined with the feedback signals from the firstsensor. The sensor feedback can also be utilized to control the movementof the workpiece relative to the laser beam to enhance the cuttingprocess control.

This apparatus, due to the collinear arrangement of the impingingsegments of the sensor and cutting beams, affords several advantages,including single-pass adaptive processing, cutting precision, andsuperior piece-to-piece repeatability. The cutting achieved is alsoindependent of cutting depth, angle of cutting, scoring patterns,material inconsistency, material color, and surface variations.

Relative motion between the workpiece and the cutting beam to cut thepiece in a predetermined pattern can be provided by different meansincluding actuators, robots and X-Y tables.

The workpiece can have a monolayer, multilayer, or compositeconstruction and can be scored on either side. The cutting can becontinuous, intermittent or be a combination of both, and extendcompletely through one or more layers of the piece. The piece can be afinished part or a component which is subsequently integrated into afinished part.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of one form of the apparatus according tothe invention including two sensors

FIGS. 2, 2A and 2B are fragmentary enlarged views of several alternativedesigns of the beam combining device incorporated in the apparatus shownin FIG. 1.

FIG. 3 is a perspective view of an automotive instrument panel with anintegrated airbag deployment door formed by in a U pattern scoringcarried out by the apparatus of the present invention.

FIGS. 4 through 6 are cross sectional views of sample monolayer andmultilayer trim piece constructions on which various types of trim pieceweakening scorings can be made by the present apparatus.

FIG. 7 is a diagrammatic view of a second embodiment of the apparatusaccording to the invention incorporating only a single sensor.

FIG. 8 is a diagrammatic view of another form of second embodiment ofthe apparatus according to the invention incorporating only a singlesensor.

DETAILED DESCRIPTION

In the following detailed description, certain specific terminology willbe employed for the sake of clarity and particular embodimentsdescribed, but it is to be understood that the same is not intended tobe limiting and should not be so construed inasmuch as the invention iscapable of taking many forms and variations within the scope of theappended claims.

This invention describes an improved apparatus for cutting a workpiecewith a laser cutting beam.

FIG. 1 shows a first embodiment of a workpiece cutting apparatus 10according to the invention. This includes a laser cutting beam source 12which generates a laser cutting beam which can be used to carry outcontrolled scoring of a surface 14 on one side of a workpiece such as aninstrument panel trim piece 16 that would overlie an airbag installationwhen installed.

The trim piece 16 is positioned on a holder which can comprise a fixture18. A first sensor 20 is provided to determine the depth of scoringproduced by the laser cutting beam B impinging onto the surface 14 ofthe trim piece 16 to score the same. The first sensor 20 and the lasercutting beam generator 12 are connected to a beam combining device 22.The beam combining device 22 (shown in detail in FIG. 2) is designed tocombine the separately generated electromagnetic sensing beam Aemanating from the first sensor 20 and the laser cutting beam B fromsource 12 so as to be in a collinear relationship and to direct thecombined segments of the sensor beam A and cutting beam B so as toimpinge the same precise spot on the trim piece surface 14. This beamcombining device 22 will also redirect any reflected beam or beamsrequired for sensor operation from the trim piece surface 14 back to thefirst sensor 20 as necessary in carrying out the process.

The trim piece 16 is moved relative to the cutting laser beam source 12,as well as the first sensor 20 and the beam combining device 22 via amotion actuator 24 drivingly engaged with the holder comprised offixture 18 to cause tracing of a particular scoring pattern on thesurface 14 and to achieve a precisely controlled rate of scoring. Themotion actuator 24 can itself directly hold and move the trim piece 16itself or move the optional fixture 18 onto which the trim piece 16 ismounted. Alternatively, the motion actuator 24 could be used to move thelaser beam source 12 and the first sensor 20 relative to the trim piece16.

A second sensor 26 may be located on the side of the trim piece 16opposite the first sensor 20, a second sensor beam emanating therefrom,directed at the outer surface 28 of the trim piece 16 and alignedopposite the same trim piece point as is the laser cutting beam and thefirst sensor beam or beams are directed in order to control the scoringso as to produce a programmed thickness of material remaining afterscoring. This is done by combining signals generated by both sensors 20,26 to create a feedback signal corresponding to the thickness of theremaining material.

The apparatus 10 is operated via one or more industrial controllers 30that control the scoring effected by the laser and/or the movement ofthe motion actuator based on a particular program and feedback signalsprovided by the sensor 20, 26.

Lasers that in particularly desirable for carrying out this type ofscoring processes are of the carbon dioxide, excimer, solid state, argongas, or diode type. However, based on the workpiece materials utilized(polymers, fabrics, wood, leather), the carbon dioxide laser is likelyto be the most preferable in terms of operability, efficiency and cost.The laser can be operated either continuously or in a pulsed mode.

Different type of sensors can be utilized to measure the extent ofmaterial removed or remaining during scoring of the trim piece. For thefirst sensor 20, connected to the beam combining device 22, a preferredtype is a closed loop device that sends and receives a specific beam ofelectromagnetic radiation in order to determine the depth of scoringeffected by the laser. The Conoprobe sensors offered by Optimet andbased on the technique of conoscopic holography, is one such sensorcommercially available. In this type of sensor, an emitted laser beamand reflected return beams of visible light have segments also travelingin a collinear relationship with each other and the laser beam. Anothertype of sensor that could be utilized is one that detects reflectedlight beams such as a high speed CCD camera. In this application, thereflected beam will be reflected from the trim piece surface beingscored by the cutting beam.

For the second sensor 26 aimed at the outside surface of the trim piece,which is generally smooth and accessible, there are more numerousoptions than electromagnetic beams and including infrared, laser,ultrasonic, conoscopic, CCD camera, proximity and contact type sensors.

The signal spot size of the first sensor beam selected can varysignificantly. Generally the smaller the spot size the better. For thefirst sensor, the preferred size would not exceed the size of thescoring produced on the trim piece by the cutting laser beam. For thesecond sensor, if surface finish variations, so called grain, aresignificant, its spot size should preferably not exceed 300 microns.

There are numerous ways for combining the separately originated cuttinglaser beam B and sensor beam A to create collinear segments thereof.FIG. 2 shows the inner details of the beam combining device 22 whichcombines the separate laser beam B and the first sensor beam A to createcollinear segments which impinge the trim piece surface 14. The beamcombining device 22 includes a reflector 32 having coatings causingreflection of light of the wavelength of the sensor beam A from itsinclined surface while allowing the cutting laser beam B to betransmitted.

Such coated selective reflectors are commercially available. This ofcourse requires that the laser and sensor beams be of differentwavelengths.

A side entrance tube 29 directed at the reflector 32 is connected to thefirst sensor 20. The main tube 31 mounts the reflector 32, main tube 31having an end opening 33 directed at the trim piece 16.

The segment of the sensor beam A reflected from the reflector 32 iscaused to be collinear, i.e., aligned and coextensive with the segmentof the laser beam B past the reflector 32, with both collinear segmentsthen impinging the surface 14 at the same precise point.

FIG. 2A shows a second form of a beam combining device 22A having aninclined reflector 32A having coatings causing reflection of a beamhaving the wavelength of the cutting laser beam B, while allowingtransmission of the beam having wavelengths of the sensor beam A to betransmitted therethrough to reverse the relationship shown in FIG. 2.

FIG. 2B is a simplified diagrammatic view of another form of the beamcombining device 22B combining the cutting laser beam B and the firstsensor beam A to produce collinear downstream segments thereof. Thisembodiment includes a simple mirror reflector 36 having a through hole34. The hole 34 is small in diameter relative to the diameter of thecutting laser beam B in order to minimize or eliminate the effect thatthe presence of the hole 34 may have on reflecting the cutting laserbeam from the mirror reflector 36 to redirect the cutting laser beam B.Such a mirror does not require coatings that are wavelength-selectivesuch as those shown in FIGS. 2 and 2A in order to combine segments ofthe beams into a collinear relationship. In this particular arrangement,the first sensor 20 could be a CCD camera receiving beams reflected fromthe trim piece surface being scored by the laser beam.

In order to apply the complete scoring pattern, the trim workpiece ispreferably moved relative to the laser beam and/or the sensors. Therelative motion can be applied by a various types of motion actuatorsincluding robots and X-Y tables. During cutting, the sensor thicknessdata can also be used to control the movement of the motion device inorder to apply the scoring along the predetermined pattern. Theworkpiece may be held directly by the motion device or be attached to aholding fixture held by the motion device. The holding fixture may beshaped to match the shape of the workpiece and/or be designed toregister specific surface features of the workpiece. Vacuum or clampscould also be applied to the holding fixture to hold the trim piecesurface in better contact with the fixture 18. The fixture 18 can bedesigned to allow the second sensor 26 to have physical and/or opticalaccess to the surface 28 of the workpiece (i.e., transparent fixturewall, opening in fixture wall, etc.).

The process controller 30 is designed to control the operation of thelaser and/or motion actuator based on the feedback signals provided bythe two sensors 20, 26 which, from opposites sides or surfaces of thetrim piece 16, monitor the location being scored. The two sensors 20, 26working in tandem determine the remaining thickness of the trim piece 16at any point they are directed to. During laser scoring at a givenpoint, the two sensors 20, 26 provide signals from which a measurementof the material thickness remaining after the scoring can be derived bythe control device 30. Based on this real-time thickness determination,the process control device 30 controls the operation of the cutting beamsource 12 to effect only the desired extent of material removal intendedfor any given point on the workpiece 16. The remaining thickness datacan also be used to control the motion actuator 24 to move the workpiece16 to the next desired location along the predetermined scoring pattern.

Due to the collinearity of the impinging segments of the first sensorbeam and the cutting beam, several advantages are realized that couldnot be attained by any of the existing processes. Since the first sensorbeam and the laser beam are always impinging on the same point on thetrim piece, the process becomes insensitive to a large number of keyvariables, including the angle of cutting, the depth of the penetration,the trim piece thickness, the configuration of the weakening patternand, to a large extent, the speed of cutting. Also, the combination ofthe two sensors provides for a direct remaining thickness measurement,superior scoring precision and excellent part to part repeatability. Inaddition, the process enables the user to overcome variations in trimpiece thickness, material properties such as density, color, voids andsurface grain. These and other benefits are obtained while operatingwith rapid adaptive control in a single-pass mode.

This apparatus can be used in various ways, such as to cut or score aworkpiece continuously or to form discontinuous cuts such as slots,grooves, etc., therein.

A second embodiment of the apparatus 44 according to the invention isshown in FIG. 7 where the outer surface 42 of the trim piece 16 is inintimate contact with the inner fixture wall 46. In this arrangement,the distance between the first sensor 48 and the fixture inner wall 46,along the predetermined scoring pattern, can be measured prior tostarting the scoring operation. If this distance can be maintainedconstant from pass to pass, then the second outside sensor would not benecessary while still running the process in a single-pass, adaptivecontrol mode.

FIG. 8 shows another embodiment of the apparatus 50 where the firstsensor 52 is mounted immediately alongside the cutting beam source 12 sothat both beams A, B are substantially collinear with each other toapproximate the effect of using the beam combining device 22 described.

The laser cutting beam may also function as the sensor. This arrangementalso maintains the collinear configuration as the sensing signals andthe laser beam are generated by the same laser. Under this approach, thelaser beam characteristics and control would be manipulated to conductsensing measurements during or between cutting intervals (i.e., sensingafter a preset number of cutting pulses).

What is claimed is:
 1. An apparatus for weakening a workpiece,comprising: a laser source for a cutting beam able to score a surface onone side of said workpiece; a holder for holding said workpiece in aposition so that said laser cutting beam is directed at said surface ofsaid workpiece; a motion actuator imparting relative motion between saidsource of said laser cutting beam and said workpiece in a predeterminedpattern; a sensor arrangement for monitoring the remaining materialthickness of said workpiece, said sensor arrangement including a firstinner sensor directing a sensing beam towards each point on saidworkpiece which is being scored by said laser cutting beam; said sensorarrangement also including a second outer sensor detecting an oppositesurface of said workpiece; a beam combiner combining said laser cuttingbeam and said first sensor sensing beam in a collinear relationship,said collinear beams continuously thereby directed at the same point onsaid workpiece; and, control means responsive to the extent of saidscoring of said workpiece at each point along said predetermined patterndetected by the monitoring of said first and second sensors tocorrespondingly adjust the scoring effect of said cutting beam toproduce a predetermined thickness of said workpiece remaining after saidscoring along said predetermined pattern.
 2. The apparatus according toclaim 1 wherein said first sensor beam source is a laser beam source. 3.The apparatus according to claim 1 wherein said first sensor beam iscomprised of electromagnetic radiation.
 4. The apparatus according toclaim 1 wherein said holder comprises a fixture shaped to provideintimate contact with said opposite surface of said workpiece.
 5. Anapparatus for cutting a workpiece, comprising: a laser source forgenerating a laser cutting beam able to cut into a surface of saidworkpiece; a holder for holding said workpiece in a position so thatsaid cutting beam is directed at a surface of said workpiece; a motionactuator imparting relative motion between said laser cutting beam andsaid workpiece to create cutting of said workpiece in a predeterminedpattern; a sensor arrangement for monitoring the extent of cuttingeffected on said trim piece by said cutting beam, said sensor located onthe same side of said workpiece as said generating a sensing beamdirected from the same side towards the point on said workpiece pointbeing cut by said cutting beam; a combiner device combining downstreamsegments of said laser cutting beam and said sensing beam to be acollinear with each other, said collinear beam segments both directed atthe same point on said workpiece; and, control means responsive to saidmonitoring of said cutting on said workpiece at each point along saidpredetermined pattern by said sensor arrangement to adjust the cuttingeffected by said cutting beam in correspondence thereto to produce apredetermined extent of cutting along said predetermined pattern.
 6. Theapparatus according to claim 5 wherein said sensing beam is a laserbeam.
 7. The apparatus according to claim 5 wherein said sensor beam iscomprised of electromagnetic radiation.
 8. The apparatus according toclaim 5 wherein said workpiece holder is a fixture shaped to provideintimate contact with surface of said workpiece opposite said surfacecut by said cutting beam.
 9. An apparatus for forming lines of weakeningin a workpiece, comprising: a laser cutting beam source producing alaser cutting beam able to score a surface of said workpiece; a holderfor positioning said workpiece so that said laser cutting beam isdirected at a surface of said workpiece; a motion actuator impartingrelative motion between said laser cutting beam source and saidworkpiece to trace a predetermined pattern on said surface; a sensorarrangement monitoring the extent of material removal effected by saidlaser cutting beam, said sensor producing a sensing beam directedtowards said surface of said workpiece; and, a beam combining devicereceiving both said cutting and sensing beams, combining respectivedownstream segments of said beams in a collinear relationship, anddirecting the combined beam segments at said surface of said workpiece.10. The apparatus according to claim 9 wherein said sensing beam is alaser beam.
 11. The apparatus according to claim 9 wherein said cuttingand sensor beams are electromagnetic radiation of different wavelengths,and said sensing and cutting beams are both directed at a reflectorwhich selectively transmits one beam and reflects the other as a resultof their difference in wavelengths to combine said beams into acollinear relationship with each other.
 12. The apparatus according toclaim 11 wherein said reflector is inclined at 45° and said one beam isdirected at a front face thereof to be reflected and the other beam isdirected at a rear face of said reflector through which it istransmitted.
 13. The apparatus according to claim 10 wherein said sensorbeam is of much smaller diameter than said cutting beam and wherein saidcutting beam is directed at an inclined reflector surface having a holeformed therein of a much smaller diameter than said cutting beam, andsaid sensor beam is directed through said hole in a direction parallelto said cutting beam after being reflected from said reflector.